Processes to convert renewable resources into transportation fuels usually involve several steps. For example, one approach is to use acids to convert carbohydrates, starches, lignins, and other biomass into sugars such as glucose, lactose, fructose, sucrose, dextrose. The catalytic hydrogenation of the carbonyl groups of a sugar like glucose (C6H12O6) can then produce a polyalcohol including sorbitol (C6H14O6).
There has been a significant effort to produce alkanes through catalytic conversion of aqueous sorbitol and other bio-generated polyols. Chen and Koenig, U.S. Pat. No. 4,503,278, convert carbohydrates such as starch, cellulose and sugar on a crystalline silicate zeolite catalyst into fuels and useful chemicals by increasing hydrocarbon size. In U.S. Pat. No. 5,959,167, Shabtai and associates use lignins in a two-stage catalytic reaction process to produce a reformulated hydrocarbon gasoline product. In US2009126260, Aravanis, et al., convert terpenes from biomass through catalytic cracking to generate suitable fuel products. Gruter, EP2034005, prepares a hydroxymethylfurfural fuel additive from biomass by dehydration with an acid catalyst. In WO2008114033, Fredriksen and Myrstad, mix bio-oil and mineral oil in an FCC cracking unit to generate bio-LPG, bio-naphtha and alkylating or catalytically polymerizing bio-LPG fraction to form a bio-gasoline. Dumesic et al., U.S. Pat. No. 7,572,925, convert sugars to furan derivatives (e.g. 5-hydroxymethylfurfural, furfural, dimethylfuran, etc.) using a biphasic reactor containing a reactive aqueous phase and an organic extracting phase. Finally in US2008173570, Marchand and Bertoncini use hydrodesulphurization of an incoming stream that is subsequently cut with plant and/or animal oils, the oil mixture is hydrotreated with specialized equipment to effluents with higher cetane ratings. Unfortunately these systems do not address current problems encountered with processing biomass to automotive fuels.
Some advances have been made toward the catalytic conversion of sorbitol to alkanes. Huber, et al., (2004) used Palladium, Silica, and Alumina catalysts to convert sorbitol to a stream of alkanes including butane, pentane, and hexane. Incorporating hydrogenation of reaction intermediates with produced hydrogen increased yield. David, et al. (2004) assayed conditions for the production of hydrogen and/or alkanes from renewable feeds including aqueous solutions of sorbitol. In a review, Metzger (2006) notes alkane production from aqueous phase sorbitol reforming is improved with a bi-functional catalyst including a metal (Pt, Pd, or the like) and acid including silica alumina with the co-production of H2 and CO2. Although the yield of alkanes could be increased up to 98% when hydrogen was co-fed with the aqueous sorbitol stream they were able to reduce CO2 production, increasing H2O production and pathway efficiency.
Previous methods are limited by size, temperature, products, and conversion rates. Unfortunately at higher temperatures and higher catalytic activity, these reactions become quickly fouled. The catalyst must be removed and replaced before sufficient volumes of fuel are processed. Thus, these reactions must be improved to meet a commercial production scale and cost effectiveness. The processes above do not remove oxygen, require expensive catalysts, are subject to fouling, and are not scalable to production levels required. Additionally, processing biomass as a common feedstock is hindered by short catalyst lifetime, increased pressures and temperatures, increased production of coke byproducts, and increased corrosiveness. These undesirable side-effects hinder mass production of renewable fuels from biomass. Although noble metals have been used for hydrotreating at lower temperatures, these expensive catalysts do not alleviate the problem of fouling and the reactions are difficult to perform on a commercial scale. A method of converting large quantities of biomass is required that does not damage catalysts and equipment during the refining process.